Electronic equipment requires a source of electrical power for operation. In electronic equipment where use mandates portability, such as electronic test equipment, batteries provide a source of electrical power that allows the equipment to be portable.
Housing batteries in a pack provides advantages over simply inserting cells singly into receiving equipment. For example, a battery pack disclosed in U.S. Pat. No. 3,887,394 issued to Kaye provides a lightweight means to easily insert a plurality of non-rechargeable battery cells into receiving equipment and to electrically connect the cells to electrical circuits in the receiving equipment. A battery pack of this nature can meet the electrical power requirements of consumer electronics with modest demands for electrical power, such as cameras, radios, and small pocket computers.
Portable electronic test equipment is often operated in an environment that is harsher than those presented by consumer electronics and by less demanding commercial electronic equipment, such as two-way portable radios. For example, electronic test equipment may fall from precarious placements needed to access test points in equipment. For example, the equipment to be tested may be located on the roof of a building or at the top of a telephone pole. A battery pack for electronic test equipment must therefore be of sufficiently rugged construction to not only absorb shocks without damaging the battery pack, but also to maintain power to the equipment while being exposed to shocks and vibration.
Prior art battery packs often have electrical contacts in the form of conductive pads that are accessible on a surface of the battery pack. The pads are held against contacts in the electrical device by a force exerted on the battery pack in the direction of the contacts. The pads of the battery packs of this type can easily lose contact with the contacts of the electrical device when the battery pack is subject to shock or vibration. A battery pack for electrical equipment subject to shock and vibration should therefore include means for absorbing shock and minimizing susceptibility to vibration to maintain continuous electrical contact with the electrical device.
Another problem with battery packs using conductive surface pads as battery contacts is their susceptibility to inadvertent shorting. Users may carry or store extra battery packs for electronic test equipment in tool bags or metal tool boxes. The conductive pads of a battery pack may inadvertently be shorted together by metal objects in the bag or by the conductive surface of the tool box. Thus, battery packs for electronic test equipment must include a means for preventing inadvertent shorting of their electrical contacts.
Many conventional battery packs are rechargeable so that they may be used over a considerable period. These battery packs require internal circuit components such as thermistors and thermal switches, to allow the batteries to be safely recharged. For example, a battery pack shown in U.S. Pat. No. 5,180,644 issued to Bresin et al. provides battery cells and associated recharging circuitry in a package suitable for use in two-way portable radios. However, the need to include circuit components in a battery pack can unduly increase the size of the battery pack. Yet the size of a battery pack is an important factor in making the equipment using the battery pack small enough to be hand-held.